In general, a small-sized hydraulic excavator used for a disassembling work inside a building, an excavating work in a narrow space such as a narrow street and thus, is known as a hydraulic excavator that is a typical example of the construction machine. This small-sized hydraulic excavator is generally called a compact excavator and is configured by a self-propelled lower traveling structure, an upper revolving structure that is rotatably mounted on the lower traveling stricture and a working mechanism that is provided on the front-part side of the upper revolving structure. Since the small-sized hydraulic excavator has a small upper revolving structure and is narrow in space for installation of onboard devices on a revolving frame, a counterweight, an engine, a cab, a fuel tank and the like are mounted on this revolving frame in a state close to each other.
Here, the fuel tank is known as configured to equip a fuel filling port into which a fuel supplying nozzle is inserted when filing fuel and a cap for closing the fuel filling port (see, for example, Patent Documents 1, 2). Here, the fuel filling port of the fuel tank is surrounded by a fuel filling opening that is located on an outer surface of the cab and the fuel filling opening is lidded by a fuel filling door.